1. Field of the Invention
The present invention relates to a screw-mount lens barrel that is detachably mounted onto a camera body via a screw mount.
2. Description of the Related Art
Screw-mount lens barrels are used in CCTV cameras such as surveillance cameras. In screw-mount lens barrels, a shift adjustment for aligning the optical axis of the lens barrel with an optical axis of a camera body (CCD), and a lens-to-body thread alignment adjustment for adjusting the rotational position (angular position) of the lens barrel relative to the camera body, are required. The lens-to-body thread alignment adjustment is for positioning, e.g., an index mark on the lens barrel or a lens-side cable extending there from to a specific angular position with respect to the camera body, since the relative rotational position (relative angular position) between the lens-side screw mount (the screw mount on the lens barrel) and the body-side screw mount (the screw mount on the camera body) is indefinite (unreliable).
Japanese Unexamined Patent Publication No. H10-115757 discloses a screw-mount lens barrel in which a shift adjustment and a lens-to-body thread alignment adjustment is possible. A lens-side mount frame that is screw-engaged with the body-side mount of a camera body is provided with a C-shaped rotation restricting groove, a lens holder frame that holds a photographing lens (photographing optical system) is provided with rotation restricting screws, and the lens-to-body thread alignment adjustment is carried out by rotating the lens holder frame relative to the lens-side mount frame with the rotation restricting screws engaged in the rotation restricting groove. In addition, the shift adjustment is carried out by moving a combination of the lens holder frame and a mount set ring relative to the lens-side mount frame in directions orthogonal to the optical axis by fixing the mount set ring to the lens holder frame in a relatively irrotatable manner and making a plurality of shift screws, which radially extend through (i.e., are screwed through) the mount set ring, contact and press against the lens-side mount frame.
However, in the above-described configuration (Japanese Unexamined Patent Publication No. H10-115757), since it is required to make the plurality of shift screws, which radially extend through the mount set ring, contact and press the lens-side mount frame while rotating the lens holder frame relative to the lens-side mount frame (since the shift adjustment and the lens-to-body thread alignment adjustment must be carried out simultaneously), these two adjustments are not very independent from each other, which complicates the operations for these adjustments, so that considerable experience is required to carry out the shift adjustment and the lens-to-body thread alignment adjustment. In addition, when only the shift adjustment or only the lens-to-body thread alignment adjustment is desired to be carried out independently, one cannot typically carry out either adjustment to a satisfactory extent.